<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box {
            width: 200px;
            height: 100px;
            padding: 20px;
            border: 5px solid black;
            margin: 10px;
            background-color: lightblue;
        }
    </style>
</head>
<body>
    <!-- 
    在标准盒模型下
    内容区大小=width x height
    可视区大小=width + padding-left + padding-right + border-left + border-right
    实际占位大小=width + padding-left + padding-right + border-left + border-right + margin-left + margin-right
    -->
    盒子模型的内容区大小
    <div class="box"></div>
</body>
</html>